Mechanical inversion process for marking silicone oil-in-water emulsions

ABSTRACT

High viscosity silicone compositions such as silicone gums, silicone rubbers, silicone elastomers, and silicone resins, are emulsified by mechanical inversion in which silicone water-in-oil (W/O) emulsions are inverted to silicone oil-in-water (O/W) emulsions. Silicone resins with a viscosity of about one billion centistoke (mm 2 /s), i.e., 1,000,000,000 centistoke (mm 2 /s) have been emulsified. These silicone O/W emulsions are useful in personal care products where they are capable of providing improved aesthetics. They are also useful in products used in the paper industry and medical industry. The silicone O/W emulsions are easier to handle than the high viscosity silicone in the emulsion, which enables the emulsions to mixed with other emulsions or other water-soluble ingredients.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage filing under 35 U.S.C. §371 ofPCT Application No. PCT/US2004/012001 filed on 19 Apr. 2004, currentlypending, which claims the benefit of U.S. Provisional Patent ApplicationNo. 60/489,405 filed 23 Jul. 2003 under 35 U.S.C. §119(e). PCTApplication No. PCT/US2004/012001 and U.S. Provisional PatentApplication No. 60/489,405 are hereby incorporated by reference.

This invention is related to a mechanical inversion process for makingsilicone oil-in-water emulsions containing high viscosity silicones.More particularly, the invention is related to silicone oil-in-wateremulsions containing silicone gums, silicone rubbers, siliconeelastomers, silicone resins, or mixtures thereof.

Silicone emulsions are well known in the art. Such silicone emulsionscan be made by processes such as (i) mechanical emulsification, (ii)mechanical emulsification by inversion, or by (iii) emulsionpolymerization. However, because of the high viscosity of some siliconessuch as silicone gums, silicone rubbers, silicone elastomers, andsilicone resins, their emulsification has for all practical purposesbeen limited to emulsion polymerization. In contrast, silicones with alow viscosity and hence a low molecular weight can easily be obtainedmechanically.

However, attempts to use mechanical methods for emulsifying siliconegums, silicone rubbers, silicone elastomers, and silicone resins, havelargely been unsuccessful, because it is difficult to incorporate asurfactant or a mixture of surfactants into the silicone gum, siliconerubber, silicone elastomer, or silicone resin. It is also difficult toincorporate water into mixtures containing high viscosity silicones, asurfactant, or a mixture of surfactants, and at the same time impartsufficient shear to cause inversion. In addition, the control ofparticle size has been limited to processes involving batch-wisemechanical emulsification in the presence of a solvent.

In contrast to the above, the present invention provides an inexpensivetechnique for producing stable emulsions containing silicone gums,silicone rubbers, silicone elastomers, and silicone resins havingcontrolled particle size. This is especially useful as it relates tosilicone resins, since silicone resins are used in many applicationsrequiring water-based delivery.

It is known that the emulsification of silicone resins of the type MQ,and blends of MQ silicone resins and silicone polymers, is difficultwhen the level of the resin is high, i.e., 20-90 percent by weight basedon the total silicone content. While direct emulsification using highshear is suitable for low viscosity blends, and emulsification bycatastrophic inversion is suitable for high viscosity blends, neither isactually suitable when MQ resins are present. This is for the reasonthat the presence of high levels of silicone MQ resins in siliconeresin/silicone polymer blends, significantly increases the oil phaseviscosity; such that direct emulsification using high shear fails toyield particle sizes needed to achieve emulsion stability. In addition,the presence of significant amounts of the silicone MQ resin renders theoil phase resistant to inversion, to the extent that often the oil phaseremains non-inverted at any water-to-oil ratio.

While mixing volatile silicone fluids, volatile organic fluids, or lowmolecular weight diluents with oil phases containing high levels ofsilicone resin can ease the process of emulsification, the presence ofvolatile and/or low molecular weight fluids and diluents may not bedesired in many applications.

The invention is directed to a method of making silicone oil-in-wateremulsions containing a silicone gum, a silicone rubber, a siliconeelastomer, a silicone resin, or mixtures thereof. According to themethod, the silicone oil-in-water emulsion is made by: (i) forming ahomogeneous oil phase containing a silicone gum, a silicone rubber, asilicone elastomer, a silicone resin, or a mixture thereof; the siliconein the homogeneous oil phase having a viscosity of at least 100,000,000(100 million) centistoke (mm²/s) to 5,000,000,000 (5 billion) centistoke(mm²/s); (ii) mixing one or more surfactants with the homogeneous oilphase; (iii) adding water to the homogeneous oil phase to form awater-in-oil emulsion containing a continuous phase and a dispersedphase, the water being added in an amount of about 0.5-10 percent byweight based on the weight of the silicone in the homogeneous oil phase;(iv) applying high shear to the water-in-oil emulsion in a twin-screwextruder having a length to diameter ratio (L/D) of at least 15, tocause inversion of the water-in-oil emulsion to an oil-in-wateremulsion; and (v) diluting the oil-in-water emulsion by adding morewater.

The method is carried out in the absence of a solvent other thansolvents present in the silicone gum, silicone rubber, siliconeelastomer, or silicone resin in (i). The silicone in the homogeneous oilphase should have a viscosity of at least 100,000,000 (100 million)centistoke (mm²/s) to 5,000,000,000 (5 billion) centistoke (mm²/s),preferably at least 200,000,000 (200 million) centistoke (mm²/s) to2,000,000,000 (2 billion) centistoke (mm²/s), and most preferably itshould consist of a silicone resin having a viscosity of at least1,000,000,000 (1 billion) centistoke (mm²/s).

These and other features of the invention will become apparent from aconsideration of the following detailed description.

DESCRIPTION

The present invention provides an effective method of emulsifyingsilicone gums, silicone rubbers, silicone elastomers, and especiallysilicone resins. This is achieved by (i) inverting a water-in-siliconeoil (W/O) emulsion and forming a silicone oil-in-water (O/W) emulsionusing only a very small amount of water, i.e., about 0.5-10 percent byweight based on the weight of silicones in the oil phase, preferablyabout 1-5 percent by weight; (ii) applying very high shear duringinversion using a twin-screw extruder having a length to diameter (L/D)ratio of at least 15, preferably at least 30, and more preferably 30-60;and (iii) carrying out the inversion without adding solvents other thansolvents present in the silicone gum, silicone rubber, siliconeelastomer, or silicone resin being emulsified.

The method is especially adapted to the emulsification of silicone gums,silicone rubbers, silicone elastomers, and silicone resins that haveviscosities of at least 100,000,000 (100 million) centistoke (mm²/s) to5,000,000,000 (5 billion) centistoke (mm²/s), preferably at least200,000,000 (200 million) centistoke (mm²/s) to 2,000,000,000 (2billion) centistoke (mm²/s). These features also distinguish the presentmethod from the method described in a copending U.S. patent applicationSer. No. 10/346,544, filed Jan. 16, 2003, entitled “Method of MakingSilicone Resin Emulsions”, assigned to the same assignee as the presentinvention.

As noted, the invention relates to silicone gums, silicone rubbers,silicone elastomers, and silicone resins. For purposes of the invention,the terms silicone rubber and silicone elastomer are consideredsynonymous, at least to the extent that both silicones are capable ofelongation and recovery. Silicone gums in contrast are capable of beingstretched, but they do not generally snap back. Silicone gums are thehigh molecular weight generally linear polydiorganosiloxanes that can beconverted from their highly viscous plastic state into a predominantlyelastic state by crosslinking. Silicone gums are often used as one ofthe main components in the preparation of silicone elastomers andsilicone rubbers.

For purposes of this invention therefore, silicone gum can be consideredto include compositions of the type described in U.S. Pat. No. 3,692,737(Sep. 19, 1972), U.S. Pat. No. 4,152,416 (May 1, 1979), U.S. Pat. No.4,885,129 (Aug. 8, 1989), and U.S. Pat. No. 5,057,240 (Oct. 15, 1991),to which the interested reader is referred.

Silicone rubbers and silicone elastomers can be considered to includecompositions of the type described in U.S. Pat. No. 4,882,377 (Nov. 21,1989), U.S. Pat. No. 5,654,362 (Aug. 5, 1997), U.S. Pat. No. 5,994,459(Nov. 30, 1999), and U.S. Pat. No. 6,015,858 (Jan. 18, 2000), to whichthe interested reader is referred.

Silicone resins can be considered to include compositions of the typedescribed in U.S. Pat. No. 2,676,182 (Apr. 20, 1954), U.S. Pat. No.4,310,678 (Jan. 12, 1982), U.S. Pat. No. 4,423,095 (Dec. 27, 1983), andU.S. Pat. No. 5,356,585 (Oct. 18, 1994), to which the interested readeris referred, as well as compositions described in more detail below.

The acronym MQ as it relates to silicone resins is derived from thesymbols M, D, T, and Q each of which represent a functionality ofdifferent types of structural units which may be present in siliconescontaining siloxane units joined by ≡Si—O—Si≡ bonds. The monofunctional(M) unit represents (CH₃)₃SiO_(1/2) and the difunctional (D) unitrepresents (CH₃)₂SiO_(2/2). The trifunctional (T) unit representsCH₃SiO_(3/2) and results in the formation of branched linear siloxanes.The tetrafunctional (Q) unit represents SiO_(4/2) which results in theformation of crosslinked and resinous silicone compositions. Hence, MQis used when the siloxane contains all monofunctional M andtetrafunctional Q units, or at least a high percentage of M and Q unitssuch as to render the silicone resinous.

Silicone resins useful herein are non-linear siloxane resins having aglass transition temperature (Tg) above 0° C. Glass transitiontemperature is the temperature at which an amorphous material such as ahigher silicone polymer changes from a brittle vitreous state to aplastic state. The silicone resin generally has the formulaR′_(a)SiO_((4-a)/2) wherein R′ is a monovalent hydrocarbon group with1-6 carbon atoms or a functionally substituted hydrocarbon group with1-6 carbon atoms, and a has an average value of 1-1.8. The siliconeresin will preferably consist of monofunctioanl (M) units R″₃SiO_(1/2)and tetrafunctional (Q) units SiO_(4/2), in which R″ is the monovalenthydrocarbon group having 1-6 carbon atoms, most preferably the methylgroup. Typically, the number ratio of M groups to Q groups will be inthe range of 0.5:1 to 1.2:1, so as to provide an equivalent wherein a inthe formula R′_(a)SiO_((4-a)/2) has an average value of 1.0-1.63.Preferably, the number ratio is 0.6:1 to 0.9:1. Most preferred aresilicone MQ resins in which the number of Q units per molecule is higherthan 1, preferably higher than 5.

The silicone resin may also contain 1-5 percent by weight ofsilicon-bonded hydroxyl radicals such as a dimethylhydroxysiloxy unit(HO)(CH3)₂SiO_(1/2). If desired, the silicone resin may contain minoramounts of difunctional (D) units and/or trifunctional (T) units.Preferred silicone resins are those having a viscosity of at least100,000,000 (100 million) centistoke (mm²/s) and a softening temperatureof less than about 200° C. The silicone resin may consist of (i)silicone resins of the type M_(x)Q_(y) where x and y have values suchthat the silicone resin contains at least more than 5 Q units permolecule; (ii) silicone resins of the type M_(x)T_(y) where x and y havevalues such that the silicone resin contains at least more than 5 Tunits per molecule; and (iii) silicone resins of the typeM_(x)D_(y)T_(p)Q_(q) where x, y, p, and q have values such that the sumof Q and T units is at least more than 5 units per molecule, and thenumber of D units varies from 0-100.

Emulsions according to the invention are prepared using a surfactant.The surfactant may be an anionic surfactant, cationic surfactant,nonionic surfactant, amphoteric surfactant, or a mixture of surfactants.Nonionic surfactants and anionic surfactants are preferred, and mostpreferred are mixtures containing an anionic and a nonionic surfactant,or a mixtures containing two nonionic surfactants. When mixturescontaining nonionic surfactants are used, one nonionic surfactant shouldhave a low Hydrophile-Lipophile Balance (HLB) and the other nonionicsurfactant should have a high HLB, such that the two nonionicsurfactants have a combined HLB of 11-15, preferably a combined HLB of12.5-14.5.

Representative examples of suitable anionic surfactants include alkalimetal soaps of higher fatty acids, alkylaryl sulphonates such as sodiumdodecyl benzene sulphonate, long chain fatty alcohol sulphates, olefinsulphates and olefin sulphonates, sulphated monoglycerides, sulphatedesters, sulphonated ethoxylated alcohols, sulphosuccinates, alkanesulphonates, phosphate esters, alkyl isethionates, alkyl taurates, andalkyl sarcosinates. One example of a preferred anionic surfactant issold commercially under the name Bio-Soft N-300. It is a triethanolaminelinear alkylate sulphonate composition marketed by the Stephan Company,Northfield, Ill.

Representative examples of suitable cationic surfactants includealkylamine salts, quaternary ammonium salts, sulphonium salts, andphosphonium salts. Representative examples of suitable nonionicsurfactants include condensates of ethylene oxide with long chain fattyalcohols or fatty acids such as a C₁₂₋₁₆ alcohol, condensates ofethylene oxide with an amine or an amide, condensation products ofethylene and propylene oxide, esters of glycerol, sucrose, sorbitol,fatty acid alkylol amides, sucrose esters, fluoro-surfactants, and fattyamine oxides. Representative examples of suitable amphoteric surfactantsinclude imidazoline compounds, alkylaminoacid salts, and betaines.

Representative examples of suitable commercially available nonionicsurfactants include polyoxyethylene fatty alcohols sold under thetradename BRIJ by Uniqema (ICI Surfactants), Wilmington, Del. Someexamples are BRIJ 35 Liquid, an ethoxylated alcohol known aspolyoxyethylene (23) lauryl ether, and BRIJ 30, another ethoxylatedalcohol known as polyoxyethylene (4) lauryl ether. Some additionalnonionic surfactants include ethoxylated alcohols sold under thetrademark TERGITOL® by The Dow Chemical Company, Midland, Mich. Someexample are TERGITOL® TMN-6, an ethoxylated alcohol known as ethoxylatedtrimethylnonanol; and various of the ethoxylated alcohols, i.e., C₁₂-C₁₄secondary alcohol ethoxylates, sold under the trademarks TERGITOL®15-S-5, TERGITOL® 15-S-12, TERGITOL® 15-S-15, and TERGITOL® 15-S40.Surfactants containing silicon atoms can also be used.

Phase inversions generally occurs when the continuous phase of adispersion becomes the dispersed phase, or vice versa. Phase inversionsin liquid/liquid dispersions are categorized as either catastrophicinversions or transitional inversions. Catastrophic inversions arecaused by simply changing the phase ratio until there is a high enoughratio of the dispersed phase that it becomes the continuous phase.Transitional inversions occur when the affinity of the surfactant forthe two phases is altered in order to cause the inversion. Theinversions occurring in this invention are catastrophic inversions.

Thus, the inversion method used to make silicone gum, silicone rubber,silicone elastomer, and silicone resin emulsions, according to theinvention, is carried out by (i) forming an oil phase containing thesilicone gum, silicone rubber, silicone elastomer, and/or the siliconeresin; (i) mixing and agitating the oil phase in a twin-screw extruder;(iii) adding a surfactant(s) to the oil phase containing the siliconegum, silicone rubber, silicone elastomer, and/or the silicone resin; and(iv) agitating and mixing the oil phase in the twin-screw extruder. Instep (v), a limited and very small amount of water is added to the oilphase containing the surfactant(s), the silicone gum, the siliconerubber, the silicone elastomer, and/or the silicone resin, in a stepwisefashion, such that catastrophic inversion occurs, and an oil-in-wateremulsion is formed.

Generally, the amount of water required in step (v) is about 0.5-10percent by weight based on the weight of the silicone present in the oilphase. Preferably, the amount of water will be about 1-5 percent byweight based on the weight of the silicone present in the oil phase.While the water can be added in 2-4 portions, addition of water in asingle portion is preferred. The initial addition of water can includethe surfactant. After the desired particle size has been reached, theemulsion is diluted with the balance of water to achieve the preferredsolids content.

High shear in a twin-screw extruder is required to induce the inversion.The twin-screw extruder should have a length to diameter (L/D) ratio ofat least 15, preferably at least 30, and more preferably a L/D ratio of30-60. If desired, inversion can also be induced using a kneaderextruder having a double-arm mixer with an extrusion screw, provided thekneader extruder is capable of functioning with the same efficiency as atwin-screw extruder. The emulsion can contain other additives such asbiocides, thickeners, and freeze-thaw stabilizer, in forming the finalcomposition. The particle diameter of the silicone in the emulsions willtypically be in a range of about 0.1 to 25.0 micron (micrometer),depending on the amount and characteristics of the surfactant andsilicone used in the preparation.

It is expected that the method of the invention is capable of formingO/W emulsions of silicone gums, silicone rubbers, silicone elastomers,silicone resins, and mixtures thereof, in which the silicone has aviscosity of at least 100,000,000 (100 million) centistoke (mm²/s) to5,000,000,000 (5 billion) centistoke (mm²/s). Preferably, the siliconecomponent(s) should have a viscosity of at least 200,000,000 (200million) centistoke (mm²/s) to 2,000,000,000 (2 billion) centistoke(mm²/s). It is also expected that the method can be carried out withoutadding a solvent other than solvents present in the silicone gum,silicone rubber, silicone elastomer, or silicone resin being emulsified.The emulsification process of the invention allows active ingredients tobe incorporated in the water or the oil phase without hindrance.

Silicone O/W emulsions according to the invention are capable ofdelivering performance properties such as controlled tack andlubrication, and assist in film formation. They can be used in coatingapplications, household, cosmetic and personal care applications, toprovide greater durability, protective qualities, water resistance, andbarrier properties. Silicone O/W emulsions for personal care productsare capable of providing good aesthetics. They are also useful inproducts intended for the paper and medical industry. Since silicone O/Wemulsions are easier to handle than high viscosity silicones, theyfacilitate mixing with other emulsions or water-soluble ingredients.

The following examples illustrate the invention in more detail. In theexamples, the twin-screw extruder had a construction similar to thetwin-screw extruder shown in U.S. Pat. No. 5,354,804 (Oct. 11, 1994), towhich the interested reader is referred. It had a length of about 56inches (1,400 millimeter), and it contained a pair of screws each havinga diameter of about one inch (25 millimeter). However, any twin-screwextruder known in the art is suitable for carrying out the process. Forexample, the twin-screw extruder can be counter-rotating or co-rotating.It may be equipped with conical twin screws or parallel twin screws. Thebarrels of the twin-screw extruder may be divided into a number of zonesand equipped with metering equipment for introducing materials along thelength of the barrel.

EXAMPLE 1 Emulsions Containing a Silicone Gum

A silicone gum having a viscosity of about 100,000,000 centistoke(mm²/s) was emulsified by pumping the high viscosity silicone gum into atwin-screw extruder. The silicone gum was a dimethylvinylsiloxyterminated polydimethylsiloxane containing about 0.14 percent ofphenylmethylsiloxane units. It exhibited a plasticity number of about55-65 mils, based on the test protocol described in the American Societyfor Testing and Materials (ASTM) Test Procedure D-926. Tergitol 15-S-5and Tergitol 15-S-40 nonionic surfactants were added to the silicone gumand mixed. A small amount of water (Water 1) was added to this premix,and the components in the premix were allowed to mix until inversion hadoccurred and an appropriate particle size had been obtained. The solidscontent of the resulting ultra-high solids silicone O/W emulsion wasadjusted by diluting it with water (Water 2) at the outlet end of thetwin-screw extruder. The process parameters are shown in Table 1.Reference to Section Numbers in Table 1 refers to points of additionalong the length of the barrel of the twin-screw extruder, where it wasequipped with inlets enabling materials to be introduced. The sectionsare further identified by distances in millimeter from the inlet end ofthe twin-screw extruder. Water 1 in Run 2 (indicated by an asterisk) wasintroduced in Section 4 at 350 mm, rather than at Section 3.

TABLE 1 Component Point of Addition Run 1 Run 2 Silicone Gum, g/minSection 1-50 mm 150 250 Tergitol 15-S-40, g/min, Section 2-150 mm 6.011.2 nonionic Tergitol 15-S-5, g/min, Section 2-150 mm 2.0 3.84 nonionicWater 1, g/min Section 3-250 mm 3.8 12.4* Water 2, g/min Section 10-950mm 18.8 26.3 Total Amount, g/min 180.6 303.7 Water Rate 1, Wt. % H₂O/2.4 4.7 Wt. % Premix Water Rate 2, Wt. % H₂O/ 11.9 9.9 Wt. % PremixScrew Speed, rpm 608 198 Weight Percent Solids 87.0 87.3 Particle Size,μm 23.4 27.9 (micrometer)

EXAMPLE 2 Emulsions Containing a Silicone Resin

A silicone resin with a viscosity of about one billion centistoke(mm²/s), i.e., 1,000,000,000 centistoke (mm²/s), was emulsified bypumping the high viscosity silicone resin into a twin-screw extruder.The silicone resin was in the form of a 70 weight percent xylenesolution of a siloxane resin copolymer consisting essentially ofmonofunctional (CH₃)₃SiO_(1/2) M units and tetrafunctional SiO_(4/2) Qunits. The MQ units were present in the silicone resin in a molar ratioof approximately 0.75:1. The silicone resin contained about 2.4 to 2.9weight percent of hydroxyl functionality based on the weight of solids.This was determined by Fourier Transform Infrared Spectroscopy (FTIR)analysis according to the test protocol described in the AmericanSociety for Testing and Materials (ASTM) Test Procedure E-168. Thetwin-screw extruder was heated to 60° C. Brij 30 a nonionic surfactantand Bio-Soft N-300 an anionic surfactant were added to the siliconeresin and mixed. A small amount of water (Water 1) was added to thispremix, and the premix was allowed to mix until inversion had occurredand an appropriate particle size had been obtained. The solids contentof the resulting ultra-high solids silicone O/W emulsion was adjusted bydiluting it with water (Water 2) at the outlet end of the extruder. Theprocess parameters are shown in Table 2. Reference to Section Numbers inTable 2 refers to points of addition along the length of the barrel ofthe twin-screw extruder where it was equipped with inlets enablingmaterials to be introduced.

TABLE 2 Component Point of Addition Run 1 Run 2 Silicone Resin, g/minSection 1-50 mm 103.4 102.4 Brij 30, g/min, nonionic Section 2-150 mm6.8 4.8 Bio-Soft N-300, g/min, Section 3-250 mm 6.0 4.3 anionic Water 1,g/min Section 4-350 mm 5.0 5.0 Water 2, g/min Section 12-1150 mm 19.619.6 Total Amount, g/min 140.8 136.1 Water Rate 1, Wt. % H₂O/ 4.3 4.5Wt. % Premix Water Rate 2, Wt. % H₂O/ 16.9 17.6 Wt. % Premix ScrewSpeed, rpm 317 317 Weight Percent Solids 82.6 81.9 Particle Size, μm0.34 0.36 (micrometer)

EXAMPLE 3 Emulsions Containing a Silicone Elastomer

A silicone elastomer prepared by the method described in U.S. Pat. No.5,654,362 (Aug. 5, 1997) was emulsified by pumping the siliconeelastomer into a twin-screw extruder. The twin-screw extruder was heatedto 30° C. Tergitol 15-S-12 a nonionic surfactant was added to thesilicone elastomer and mixed. A small amount of water (Water 1) wasadded to this premix, and the premix was allowed to mix until inversionhad occurred and an appropriate particle size had been obtained. Thesolids content of the resulting silicone O/W emulsion was adjusted bydiluting it with water (Water 2) at the outlet end of the twin-screwextruder. The process parameters are shown in Table 3. Reference toSection Numbers in Table 3 refers to points of addition along the lengthof the barrel of the twin-screw extruder where it was equipped withinlets enabling materials to be introduced.

TABLE 3 Component Point of Addition Run 1 Run 2 Silicone Elastomer,g/min Section 1-50 mm 218.0 350.0 Tergitol 15-S-12, g/min, Section 2-150mm 5.4 8.2 nonionic Water 1, g/min Section 3-250 mm 3.7 4.0 Water 2,g/min Section 12-1150 mm 19.6 43.8 Total Amount, g/min 246.7 406.0 WaterRate 1, Wt. % H₂O/ 1.7 1.12 Wt. % Premix Water Rate 2, Wt. % H₂O/ 8.812.2 Wt. % Premix Screw Speed, rpm 1200 1200 Weight Percent Solids 90.688.2 Particle Size, μm 17.4 23.7 (micrometer)

Other variations may be made in compounds, compositions, and methodsdescribed herein without departing from the essential features of theinvention. The embodiments of the invention specifically illustratedherein are exemplary only and not intended as limitations on their scopeexcept as defined in the appended claims.

1. A method of making a silicone oil-in-water emulsion comprising thesteps of: (i) forming a homogeneous oil phase containing a silicone gum,a silicone rubber, a silicone elastomer, a silicone resin, or a mixturethereof; the silicone in the homogeneous oil phase having a viscosity ofat least 100,000,000 (100 million) centistoke (mm²/s) to 5,000,000,000(5 billion) centistoke (mm²/s); (ii) mixing one or more surfactants withthe homogeneous oil phase; (iii) adding water to the homogeneous oilphase to form a water-in-oil emulsion containing a continuous phase anda dispersed phase, the water being added in an amount of about 0.5-10percent by weight based on the weight of the silicone in the homogeneousoil phase; (iv) applying high shear to the water-in-oil emulsion in atwin-screw extruder having a length to diameter L/D ratio of at least15, to cause inversion of the water-in-oil emulsion to an oil-in-wateremulsion; and (v) diluting the oil-in-water emulsion by the addition ofwater; the method being carried out in the absence of a solvent otherthan solvents present in the silicone gum, silicone rubber, siliconeelastomer, or silicone resin in (i).
 2. A method according to claim 1wherein the silicone in the homogeneous oil phase has a viscosity of atleast 200,000,000 (200 million) centistoke (mm²/s) to 2,000,000,000 (2billion) centistoke (mm²/s).
 3. A method according to claim 1 whereinthe silicone in the homogeneous oil phase has a viscosity of at least1,000,000,000 (1 billion) centistoke (mm²/s).
 4. A method according toclaim 1 wherein the silicone in the homogeneous oil phase is a siliconeresin.
 5. A method according to claim 1 wherein the amount of wateradded in (iii) is about 1-5 percent by weight based on the weight of thesilicone in the homogeneous oil phase.
 6. A method according to claim 1wherein the L/D ratio of the twin-screw extruder is 15-60.
 7. A siliconeoil-in-water emulsion prepared according to the method defined inclaim
 1. 8. A personal care product, medical product, coating product,household care product, or product for application to paper, containingthe silicone oil-in-water emulsion prepared according to claim 7.